LONG-TERM PERFORMANCE OF PRECISION CRYSTAL-OSCILLATORS IN A NEAR-EARTH ORBITAL ENVIRONMENT

The Navy Navigation Satellite System (NNSS) uses precision quartz crys tal oscillators to provide time and frequency in the orbiting spacecra ft. The frequency changes for multiple oscillators, which were observe d for 28 years of operational service in the orbital environment, are discussed in this paper. The primary frequency changes are believed to be caused by mass transfer to and from the resonator, stress relief i n the resonator mounting structure and electrodes, and ionizing radiat ion of the quartz resonator [1]. Observations to a resolution of 10(-1 3) have been made from 1963 to 1991 on 20 operational satellites in ne ar-Earth orbit. No oscillator failures have occurred during the entire program life of nearly 30 years. One oscillator provided continuous o perational service for over 21 years, and several have served more tha n 15 years. No oscillator changed frequency more than two parts in 10( 7) while in operational service. One of the best performing oscillator s had a predictable drift rate of 9 X 10(-13) +/- 1 X 10(-13) per day after three years of service.